With the increasing demand for night vision surveillance in the security video surveillance system project, infrared cameras have entered the mainstream market of cameras, and the sales volume is increasing day by day. Problems in the application of infrared night vision technology are gradually exposed. This article makes a brief discussion on the technical issues of infrared cameras and the precautions during the selection, in order to share with the industry.
We all know that the application of night vision technology in the military has been for a long time. With the development of technology, it has also been widely used in civil video surveillance. In fact, night vision technology is an optoelectronic technology that enables nighttime observation by means of optoelectronic imaging devices. It includes low-light night vision and infrared night vision: low-light night vision technology is a kind of night vision technology with image enhancement tube, which actually enhances the weak target image illuminated by night light for observation. Photoelectric imaging technology.
Low-light night vision device is the largest and most versatile night vision equipment in foreign countries. It can be divided into direct observation (such as night vision viewer, weapon sight, night driving instrument, night vision glasses). Indirect observation (such as low-light TV); infrared night vision technology is divided into active infrared night vision technology and passive infrared night vision technology. Passive infrared night vision technology is an infrared technology that realizes observation by means of infrared radiation emitted by the target itself. It finds the target according to the temperature difference or heat radiation difference between the target and the background or the parts of the target, and the corresponding equipment is a thermal imager. Here mainly talk about active infrared night vision technology, which is a kind of night vision technology that realizes observation by actively illuminating and utilizing the infrared light of the target reflection infrared source. The corresponding equipment is active infrared night vision apparatus, and the actual core is the infrared camera.
The combination of the infrared light source, the camera composed of the non-direct-view photoelectric imaging device CCD or CMOS image sensor and the lens required for the imaging picture are the three factors that dominate the infrared camera nighttime monitoring effect. In order to obtain good nighttime monitoring quality, this article will focus on several points that should be paid attention to when selecting infrared cameras, their infrared light source, camera and their lenses, etc., for the reference of engineering and other users.
First, the choice of infrared light source
Infrared light is an invisible light having a wavelength greater than 780 nm. Generally, there are three methods for producing such invisible light.
1. Direct use of infrared light from incandescent or xenon lamps. That is, the visible light filter is installed on the two lamps to filter out the visible light, and only the invisible infrared rays are emitted;
2. Infrared light emitting diode LEDs or LED arrays are used to generate infrared light. Such devices generate infrared light by recombining electrons and holes in a gallium arsenide (GaAs) semiconductor;
3. The infrared laser diode LD can also be used as an infrared light source. However, it is necessary to excite or pump electrons in a lower energy state to a higher energy state, and maintain the stimulated radiation infrared light by reversing a large amount of particle distribution and resonating.
The first type of light source is a thermal infrared light source, and its greatest advantage is that it can be made into a relatively large power and a large irradiation angle, so that the irradiation distance is long. The biggest shortcoming is that it contains visible light components, that is, there is red storm, and the service life is short. If you work 10 hours a day, 5000 hours can only be used for more than one year. If you consider insufficient heat dissipation, the life expectancy is short. In order to improve the life of the heat radiation infrared lamp, a light control switch circuit must also be used in order to reduce the working time. In addition, a delay switch circuit has been added to prevent ambient light interference.
The second is an infrared lamp composed of a semiconductor gallium arsenide LED array, especially an array-type integrated light-emitting chip LEDArray that is now developed using a new technology. Its LED-Array has an optical output of 800mw-1000mw, which has become a replacement for ordinary LEDs. The LED-Array has a half-power angle of 10-120° (variable angle). Since the LED-Array is a highly integrated LED and the size is only one penny coin, it can evenly illuminate the entire space indoors, with a life of 50,000 hours. It was originally used in aviation aircraft. In recent years, due to the development of the civilian night monitoring market, LED-Array has gradually moved to the civilian market, becoming an ideal choice for high-quality night monitoring.
Although infrared LEDs and LED-Arrays have eliminated thermal infrared light sources, infrared LD light sources have to be selected for monitoring ultra-long-range scenes of more than 1 km. Because semiconductor lasers have higher brightness and better directivity than LEDs.
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